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Practitioners can construct their own video/digital imaging systems
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With the advent of computer technology, many exciting new tools have emerged for eye care.
Perhaps the most exciting development has been an application that has gotten the least attention. Video/digital imaging (V/DI) seems to be a well-kept secret. V/DI is made possible by connecting a slit lamp to both a TV/VCR and a computer. It can enhance clinical care, is an efficient teaching tool for patients and creates an atmosphere of wonder and awe. Any image that is seen with the microscope can be shared with the TV and the computer.
While many companies provide a service to make this system available, the doctor who is more technically inclined may create such a system by purchasing the parts and putting them together. This article will instruct in the construction of V/DI, guide in the purchase of software and hardware, teach the method of photography for the V/DI and describe the advantages of V/DI.
Connecting necessary elements
Compatible elements: The Topcon IIe with 50/50 beamsplitter and the Sony 107 CCD camera work well together.
The elements of the system include:
- a slit lamp with a compatible beamsplitter;
- a charged coupling device camera (CCDC), which is a sophisticated camcorder;
- a TV and a VCR that readily accept the CCDC signal;
- a video capture card - also called a capture board or a digitizer - which converts the TV signal from the CCDC to a signal that the computer understands; and
- a computer.
It is amazingly simple to connect these devices. A first important step is to check with your slit lamp supplier to determine whether a 50/50 beamsplitter is available. It is preferable to have one with an I/O switch that can disable the beamsplitter and with f-stops to change the output from the beamsplitter.
The beamsplitter is attached by simply connecting threaded tubes. Inquire if the beamsplitter is C mount capable, which means that the threaded tube from the beamsplitter can attach to the CCDC (or a teaching tube or 35-mm camera).
The CCDC is attached to the beamsplitter using threaded tubes. Connecting the CCDC to the power supply and the output cables is not difficult, but may require reading the set-up directions. The CCDC produces a TV-like signal. The output cable from the CCDC plugs into the TV and/or the digitizer. When this is accomplished, the TV and the computer can "see" everything that the doctor sees with the slit lamp.
The CCDC can produce two types of signals. One is a two-prong signal called composite. The two-prong can connect directly into a TV/VCR. The other is a multiprong signal that keeps colors separate, called S-video, and is slightly superior.
Some low resolution capture devices accept composite signals and are extremely convenient and inexpensive. They connect to the computer via a parallel port and can share a parallel port with a printer if the port is bi-directional. They also may have a two-prong port allowing the signal to be sent to the TV/VCR. Better capture cards accept S-video and connect to the motherboard of the computer. A computer consultant may be helpful to see what slots are available and to connect the capture card.
Adequate illumination
It is essential that the illumination provided by the slit lamp/beamsplitter be optimal for the CCDC.
Different CCDCs have different illumination requirements. They also have different resolution capacities and costs. A system of instruments that has demonstrated compatibility is the Topcon IIe with 50/50 beamsplitter and the Sony 107 CCDC. If another slit lamp/beamsplitter is used with the Sony 107 CCDC (which has a minimum requirement of 4.5 lux), ask if the light provided is similar to the light provided by the Topcon IIe with a 50/50 beamsplitter. If the slit lamp/beamsplitter produces less light than the Topcon combination, consider a CCDC that has a lower minimum lux requirement.
The resolution required to make a good digital image is 400 lines or greater. The CCDC resolution is also a function of the size and number of chips. A single chip of 1/3 inch on the CCDC is adequate.
It is important that the CCDC is C-mount compatible and can produce a two-prong composite signal to be attached to the TV/VCR or can produce S-video, if an S-video digitizer is chosen. If other slit lamps, beamsplitters or CCDCs are chosen, consult with an ophthalmic instrument technician regarding compatibility.
Modifications, compromises
The system described above will work for most patients with the lowest rheostat setting of the Topcon IIe slit lamp. There are some circumstances that require modifications or compromises. The system described is most versatile to these modifications.
If the illumination is too bright for the patient, a Polaroid filter can be placed over the mirror of the slit lamp light source. This will produce a compromised digital and video image. Temporarily boosting the slit lamp illumination will allow a digital capture without compromise; the focus and alignment are made with a smaller slit beam under lower illumination and the patient is instructed to close his or her eyes immediately after the signal is digitized.
If the illumination is dim for the doctor (as with posterior pole V/DI through NS 3), the slit lamp rheostat may be boosted and/or the I/O switch can be used to disable the beamsplitter. If people in the exam room are not prepared to see a problem that the doctor suspects is present (as in diabetic retinopathy), the I/O switch can also be employed.
If the illumination to the digitizer is too bright (as with anterior segment V/DI or posterior segment V/DI of children or aphakes), the Polaroid filter over the slit lamp light source can be used or the f-stops on the beamsplitter can be used. The digitized images can also be adjusted somewhat for illumination and contrast using the software, which can be adjusted with the digitizer.
Digitizers
Digitizer
options: Some digitizers plug into a parallel port and have a two-prong output jack called "video through."
Many capture card devices are available and can be purchased at computer stores. Those that are especially helpful in eye care will fulfill the follow requirements:
- Allows variable image sizes from 640 x 480 to 1280 x 960.
- Produces an image within 10 seconds (also depends on the computer components).
- Allows for 16-bit color images or greater. (Humans cannot see the difference above 16-bit, however.)
- Allows for multiple images to be present on the computer screen before saving images to the computer hard drive.
- Allows for adjustments of color, contrast and illumination to be made before saving.
- Prints before saving.
- Conveniently captures an image by touching a touch pad mouse located at the slit lamp table, depressing a foot switch or hitting the space bar placed within reach of the slit lamp.
- Captures single images within 1/60 second or less.
- Saves images in a format that is not memory intensive and is compatible with other applications such as e-mail (for example, JPG format).
One example of a digitizer that fulfills these criteria and plugs into a parallel port is Snappy by Play Inc.
Computer requirements
Most computers purchased within the past few years will not need to be modified other than setting the resolution to high and the color to 16 bit. Digital image quality and computer function is efficient with the following:
- Pentium 166 or higher (Intel processors may perform best)
- 17-inch screen with 0.28-dot pitch
- 4 megs of video RAM
- 64 megs of RAM
- 3.2 gigs of hard drive memory (1 gig for the computer and 2.2 for more than 2 years' worth of storage)
- The image quality with lower end capture cards is between Polaroid and 35 mm; with better capture cards quality is similar to 35 mm. For lower resolution capture devices, a bi-directional parallel port or available parallel port is required. For higher resolution capture cards, a slot must be available on the motherboard.
- A tape back-up system
Creating video, digital images
Anterior segment V/DI is simple. The slit beam should be opened widely and the light source should be 45º+ from the slit lamp line of sight. For posterior segment V/DI, alignment of the slit lamp, light source, 78-D lens holder and the patient is difficult and requires patience until the procedure is mastered. The patient must be still. Pupils need to be well dilated. Expect proficiency after a month and a challenge before that time. A lens holder is required because one hand is on the slit lamp joystick and the other is used to signal the capture. The 78-D lens must be centered over the pupil and held close to the patient.
The CCDC can be placed on either side of the beamsplitter, which corresponds to the right or left ocular view of the slit lamp. It is preferable to place the CCDC on the side of the doctor's dominant eye. The light source of the slit lamp is placed on the side opposite the CCDC side and 5° to 8° from the slit lamp optical line of sight.
When the slit lamp exam commences, the doctor can activate the VCR via remote control. As the exam proceeds, everything seen through the ocular is displayed on the TV. When the exam is completed, it can be replayed for the patient.
Capturing an image
On-screen image: When the capture signal is made, the image appears as a window on the computer screen. The best images can be selected, moved and adjusted with the software for contrast, illumination or color; cropped; printed and saved onto the hard drive of the computer.
When the doctor sees an image intended to be captured, the digitizer is activated by depressing a foot switch, touching the space bar on the chairside keyboard of the computer or by touching a touchpad mouse that is placed on the slit lamp table. This is the equivalent of depressing a button on a normal camera.
The doctor may look either to the TV to focus the image or can look through the appropriate ocular of the slit lamp (the one with the CCDC). Small adjustments in the position or rotation of the clear 78-D lens can have a big effect on image quality.
When the capture signal is made, the image appears as a window on the computer screen. Many images can be taken this way, only limited by the video RAM. They appear as windows slightly staggered and stacked one on top of another. The best images can be selected; moved by dragging them as windows on the screen; adjusted with the software for contrast, illumination or color; cropped; printed; and saved onto the hard drive of the computer. All this is accomplished with the software menu that comes with the digitizer.
The doctor can draw a three-dimensional representation onto the images, which are printed. If patients relocate, images can be sent as e-mail or transferred to a 3.5" disk. Images can be stored using last name, first name, month, year and right or left eye.
Stereodimerimages
Stereodimerimages can be created by having the second image taken at another position. Rotating the slit lamp source with the slit lamp oculars so the right ocular is placed where the left ocular previously was when the first image was taken will accomplish this goal. Images are dragged side by side. By converging or using prism lenses, the doctor can see a three-dimensional image similar to that seen with the slit lamp.
When stereoimages are stored, one more designation is added: "r" for the image taken by the right ocular position and "l" for the left ocular position.
Stored images from previous exams are presented on the screen by using the "find" function via the "start" menu of Windows 95. Storage and retrieval of images can be delegated to an assistant.
Advantages
A picture is worth 1,000 words. It becomes so much easier to explain giant papillary conjunctivitis, infiltrates, basal cell carcinoma, acne rosacea, arcus and vitreous degeneration with photography. These photos do not need to be sent out for development and do not require a flash or consumable film.
This system also creates an atmosphere of awe, and patients are impressed. Any stereoimaging of the optic nerve will catch glaucoma at an earlier stage, usually before it shows on threshold field studies.
Cost, tips, alternative methods
Beamsplitter costs are approximately $2,200. CCDCs are approximately $1,700. Video capture cards are approximately $250. Better cards are approximately $1,000. Purchase gold-plated wiring to improve image quality. These are inexpensive.
Place the TV/VCR where the patient will not be distracted during the exam. Plan on consulting with your instruments supplier regarding the CCDC and the beamsplitter. Plan also on needing help from your computer consultant.
Complete systems available
If you are not a do-it-yourselfer, consider purchasing a complete system including set-up and training instead of constructing this on your own. The EPIC system by Optronics Engineering and the ReSeeVit system by Veatch Instruments offer excellent packages. BioVID, a less expensive and less efficient system (available with a 15-day, risk-free trial) is offered by LW Scientific. Synemed and Topcon might help you build a system.
Whatever the system, video and digital imaging will be a welcome and exciting addition to your practice.
For Your Information:
- Matthew Kelleman, OD, is in primary care practice in central New Jersey. He can be contacted at e-mail: LKelleman@compuserve.com. Dr. Kelleman has no direct financial interest in the products mentioned in this article, nor is he a paid consultant for any company mentioned.
- Topcon America Corp. can be contacted at 65 West Century Road, Paramus, NJ 07652; (201) 261-9450 or (800) 942-6667; fax: (201) 387-2710.
- Snappy is available from Play Inc., (800) 306-PLAY.
- EPIC is available from Optronics Engineering, 175 Cremona Drive, Goleta, CA 93117; fax: (714) 249-9552.
- ReSeeVit is available from Veatch Instruments, 136 West Orion Street, #3, Tempe, AZ 85283; (800) 447-7511.
- BioVID is available from LW Scientific Inc., at 4727-G N. Royal Atlanta Drive, Tucker, GA 30084; (800) 726-7345; www.lwscientific.com.
- Synemed can be contacted at 4562 East Second Street, Benicia CA 94510; (707) 745-8386; (800) 777-0650; fax: (707) 745-6409.